FIG. 4.
Analysis of short A7 transcripts initiated at wild-type and mutant upp promoters. DNA templates containing either the wild-type (T8) or a Tn mutant promoter were transcribed in vitro in reaction mixtures containing 200 μM each [γ-32P]ATP, CTP, and GTP and 1,000 μM UTP. The autoradiograph is of the 25% polyacrylamide gel used to separate the transcripts. The lengths (in nucleotides) of transcripts with the sequence AUn (where n is ≥3) are shown on the left. The lengths of transcripts produced by simple abortive initiation are shown on the right. Note that the identity of the minor 5-mer transcript initiated at the T4 promoter is unknown. Also note that the AU2GU transcript, which is produced by simple abortive initiation at the T2 promoter, comigrates with the AU3G transcript initiated at the T3 promoter. Unlabeled transcripts initiated at the T2 promoter are discussed in the text.